This work investigates the surface dislocation mechanism of platinum nanoparticles in smaller–is–weaker regime. While 12–nm silica–coated (surface diffusion is limited) nanoparticles show minimal increase in yield strength compared with 12–nm bare nanoparticles, 16–nm (surface is less curved than smaller nanoparticles) bare nanoparticles show significantly greater yield strength. This suggests that diffusive thermal factor plays less important role than geometrical athermal factor in surface dislocation nucleation.